The unifying goal of our proposed studies is to further develop tandem mass spectrometry (MS) as an analytical method for the multiplex analysis of enzyme activities of diagnostic value for the detection of inborn errors of metabolism. Tandem MS assays will be developed for the enzymes relevant to the lysosomal storage diseases (LSD) belonging to the Mucopolysaccharidosis groups II (MPS-II, Hunter), MPS- VI (Maroteaux-Lamy), and metachromatic leukodystrophy, using dried blood spots on newborn screening cards as the enzyme source. Treatment of these disorders is in late-stage development, and our assays will make it possible for newborn screening laboratories to spot these diseases prior to the development of irreversible phenotypic abnormalities. Another group of diseases to be tackled is the Sanfilippo syndromes A-D (Mucopolysaccharidosis IIIA-D). The biochemical analysis of Sanfilippo syndromes is difficult because the same phenotypic symptoms present in patients when one of the four different enzymes is deficient. Furthermore, previous assays of the relevant enzymes have been difficult owing to the need to use a collection of different assay techniques. Tandem MS assays of all four enzymes relevant to Sanfilippo syndrome will use the same single analytical platform as for the otherLSD. We will develop assays for enzymes in the heme biosynthetic pathway for the biochemical diagnosis of the various forms of porphyrias. Porphyrias are not typically assayed in most clinical laboratories because of the need for highly specialized protocols. We will attempt to develop tandem MS assays for all of the individual enzymes in the heme biosynthetic pathway so that the assay can be carried out in a larger number of laboratories, which will help physicians diagnose this set of disorders.